Problem 100 - Objective Biology for NEET

Question

Select the incorrect statement from the following: (a) A physical change simply refers to a change in shape without breaking of bonds. (b) Change is a state of matter and it is also a physical change. (c) Hydrolysis of starch into glucose is an inorganic chemical reaction. (d) Catalyzed reactions proceed at rates vastly higher than that of uncatalyzed ones.

Step-by-Step Solution

Answer

The incorrect statement is (b): 'Change is a state of matter and it is also a physical change.'

Step 1: Investigating statement (a)

The first statement says that 'A physical change simply refers to a change in shape without breaking of bonds.' This is a correct definition of a physical change in the context of chemistry, where changes of state, temperature, or shape do not create new substances and no chemical bonds are broken or formed.

Step 2: Investigating statement (b)

The second statement asserts that 'Change is a state of matter and it is also a physical change.' This statement is incorrect because change is neither a state of matter nor a physical change. The three common states of matter are solid, liquid, and gas, and change refers to a alteration from one state to another or a difference in physical properties. Thus, this statement is the incorrect one.

Step 3: Investigating statement (c)

The third statement suggests that 'Hydrolysis of starch into glucose is an inorganic chemical reaction.' However, this statement is true. Hydrolysis is a type of chemical reaction, more specifically, it's an organic reaction rather than an inorganic one, as it involves the breaking of a compound due to the reaction with water, making this statement true.

Step 4: Investigating statement (d)

The fourth statement proclaims that 'Catalyzed reactions proceed at rates vastly higher than that of uncatalyzed ones.' This is also a correct statement, as catalysts work by lowering the activation energy of a reaction, therefore increasing the rate at which it happens.

Key Concepts

Physical Change

A physical change involves alterations in the form or appearance of a substance without changing its chemical composition.
This means that no new substances are formed during a physical change.
Examples include melting ice, tearing paper, or dissolving sugar in water.

• Shape change: Alterations like bending or stretching that do not affect the material's chemical nature.
• State change: Transitions between solid, liquid, and gas phases.
• No breaking of chemical bonds: The molecules remain intact though their arrangement or physical state might shift.

Physical changes are usually reversible, meaning the original material can be recovered without creating or destroying molecules.

Chemical Reaction

A chemical reaction involves the transformation of substances into new products through the breaking and forming of chemical bonds.
Indicators of chemical reactions include color changes, gas production, or the formation of a precipitate.

• Reactants and Products: Original substances transform into new ones.
• Bond Formation and Breaking: Essential for creating new chemical structures.
• Energy Changes: Reactions may absorb (endothermic) or release (exothermic) energy.

Everyday examples are rusting iron, burning wood, or baking a cake.

States of Matter

The states of matter refer to the different forms in which substances can exist: solid, liquid, and gas.
These states are determined by temperature and pressure conditions.

• Solid: Molecules are tightly packed, giving a definite shape and volume.
• Liquid: Molecules are less tightly packed than solids, allowing movement and taking the shape of the container.
• Gas: Molecules are widely spread and move freely, with no definite volume or shape.

Changes in state, such as freezing, melting, or boiling, are examples of physical changes and do not alter the chemical nature of the substance.

Catalysis

Catalysis is the process of increasing the rate of a chemical reaction by adding a catalyst.
The catalyst itself remains unchanged after the reaction.

• Activation Energy Reduction: Catalysts lower the energy barrier for a reaction, making it proceed faster.
• Enzyme Catalysis: Biological catalysts that speed up vital body reactions, like digestion and metabolism.
• Heterogeneous and Homogeneous Catalysis: Distinction based on whether the catalyst is in a different phase than the reactants or the same.

Catalysis is crucial in industrial processes, often enabling energy-efficient production methods.